Abstract

Protein adsorption on nanoparticles has become fundamental in a variety of applications including drug delivery, nanoparticle-based biosensors and environmental biotechnology. However, the fundamental principles behind protein adsorption at the solid-liquid interface, especially nanoparticles, is not completely understood. This is due to the wide range of proteins and their subsequent wide range of interactions with different nanomaterials. In this study, the interactions between proteins and gold nanoparticles was investigated with emphasis on optimising a method for protein quantitation, comparing the adsorption of a range of differently sized proteins and investigating the effect of protein adsorption onto gold on enzymatic activity. We showed that the analytical method ICP-AES was highly applicable for protein quantitation with many advantages over more conventional techniques. Similarly, the Bradford assay and Nano Orange fluorescence assay proved capable of accurate protein quantitation and given their simplicity and wide availability are ideal for quick adsorption analysis. We also show that the ability to form Au-S bonds is highly advantageous for protein interactions with gold nanoparticles demonstrated by the adsorption of GST which adsorbed to a much higher extent than the other proteins investigated due to the presence of four thiol groups. Moreover, optimising the adsorption of a particular protein requires specific conditions shown by the inability to measure cytochrome C adsorption at a neutral pH. Finally, we showed that adsorption onto gold has a significant impact on enzymatic activity verified by the decrease in HRP activity upon adsorption onto the surface. Importantly, the activity did not completely deplete suggesting the potential use of enzyme immobilisation on gold nanoparticles.